Ratan Tiwari

Allelic variations of functional markers for polyphenol oxidase (PPO) genes in Indian bread wheat (Triticum aestivum L.) cultivars.

Polyphenol oxidase (PPO) activity causes undesirable browning and discolouration of products manufactured from bread wheat (Triticum aestivumL.) during processing or storage. PPO is a copper-containing metalloprotein which catalyses hydroxylation of o-monophenols to o-diphenols and oxidation of o-diphenols to o-quinones. Auto-oxidation and polymerization of quinones with amino acid group of cellular proteins results in dark and brown discolouration of products made from bread wheat grains (Anderson and Morris 2001). The darkening phenomena of such products may reduce the quality of products and thus affect consumer acceptance. Flour protein content has a negative association with flour PPO activity (Park et al. 1997) presumably because of reactivity of phenolic side groups (Demeke et al. 2001). In wheat, PPO genes belong to a multi-gene family and are classified into two clusters: kernel and nonkernel, based on gene expression sites (Anderson et al. 2006; Jukanti et al. 2006). Recently, Massa et al. (2007) reported 21 distinct PPO sequences in kernel-type genes in wheat and wild relatives. Many studies have implied that PPO activity is mainly conditioned by the genes located on homoeologous group 2 chromosomes in wheat and wild relatives (Demeke et al. 2001; Watanabe et al. 2004, 2006; Sun et al. 2005; He et al. 2007, 2009; Raman et al. 2007). The high activity PPO alleles on chromosomes 2AL and 2DL are most thoroughly studied and were first reported by Wrigley and McIntosh (1975). A relatively low PPO activity was also found to be associated with chromosomes 2B, 3D and 6B (Demeke et al. 2001; Fuerst et al. 2008). Functional Sequence tagged site (STS) markers for PPO genes on chromosomes 2A and 2D have been developed, based on DNA sequences in GenBank (Sun et al. 2005; He et al. 2007;

Molecular investigations on grain filling rate under terminal heat stress in bread wheat ( Triticum aestivum L.)

Grain yield under post anthesis high temperature stress is largely influenced by grain filling rate (GFR). To investigate molecular basis of this trait, a set of 111 recombinant inbred lines (RILs) derived from Raj 4014, a heat sensitive genotype and WH 730, heat tolerant cultivar was phenotyped during 2009-2010 and 2010-2011 crop seasons, under field conditions. The difference in GFR (dGFR) between the timely and late sown conditions was used as a phenotypic parameter to find association with molecular markers, as parental lines exhibited significant difference for this trait. The mapping population showed clear-cut segregation pattern for differences in GFR between timely and late sown conditions. About 75% of the progenies showed no difference while 25% showed significant difference in GFR under high temperature stress created by late sown condition. To study the association of this trait with the markers, the parental lines were screened with 300 simple sequence repeat (SSR) microsatellite markers out of which 15% (45) were polymorphic between parental lines. These polymorphic markers were utilized for genotyping a subset, comprising of 43 RILs that had clear contrasting variation for dGFR. Regression analysis revealed significant association of dGFR of RILs with two markers viz., Xbarc04 and Xgwm314 with coefficients of determination (R2) values of 0.10 and 0.06, respectively. Keywords : Grain filling rate (GFR), simple sequence repeat (SSR), heat tolerance, wheat African Journal of Biotechnology Vol. 12(28), pp. 4439-4445

Association of SSCP variants of HSP genes with physiological and yield traits under heat stress in wheat

Heat stress alters various physiological phenomenons which adversely affect yield components and ultimately lead to a severe reduction in economic yield in wheat (Triticum aestivum L.). To cope with heat stress, plants have army of heat shock proteins (HSPs) which acts as molecular chaperones stabilizing the polypeptides and membranes. The thermo-tolerance ability of different genotypes of a plant species resides in their genetic diversity of HSP genes. In this study, association of HSPs with physiological and yield traits under heat stress was investigated. Results showed that wheat genotypes differed significantly in their response to high temperature. Single-strand conformation polymorphism (SSCP) analysis of targeted coding sequence of different HSP genes produced seven different haplotypes from HSP 16.9, while only two haplotypes were produced from HSP 23.5, HSP 90a and HSP 90b. Among 25 SSCP variants detected in HSP 16.9 targeted coding sequence, 12 were polymorphic and three of them were found significantly associated with canopy temperature (CT), relative water content (RWC), thousand grain weight (TGW) and normalized difference vegetation index (NDVI). These associated alleles explained 11.4 to 32.9% of the variation for individual trait. The association between HSP variants and these traits may provide new insight for HSPs potential contribution to thermo-tolerance which can be used for improvement of thermo-tolerance in wheat through marker assisted selection.

Draft Genome Sequence of Two Monosporidial Lines of the Karnal Bunt Fungus Tilletia indica Mitra (PSWKBGH-1 and PSWKBGH-2)

ABSTRACT Karnal bunt disease caused by the fungus Tilletia indica Mitra is a serious concern due to strict quarantines affecting international trade of wheat. We announce here the first draft assembly of two monosporidial lines, PSWKBGH-1 and -2, of this fungus, having approximate sizes of 37.46 and 37.21 Mbp, respectively.

Metagenomics of wheat rhizosphere for abiotic stress management

Plant microbiome also known as it’s second or extended genome, regulates and influences plant’s metabolism and growth. The plant microbiome members promote nutrient uptake, tolerance against abiotic and biotic stresses and regulate host immune system. Although there is plenty of information available on role of rhizosphere microbiome for plant growth, but still there is dearth of knowledge for the vast majority of rhizosphere microorganisms. This is mainly due to their unknown growth requirements or inability to grow on any known growth media. To support plant growth under stress conditions, the information on presence of specific microorganism in rhizosphere microbiome along with the role it plays is very much essential. Here, we review the generalized role of plant microbiome in different plant functions, information generated till date specifically on wheat metagenomics, role of rhizosphere microorganisms in abiotic stress management in other crop plants and the breeding in wheat in light with wheat metagenomics or metagenome engineering through breeding.

Putative Markers associated with Grain weight under Terminal Heat Stress in Bread-Wheat (Triticum aestivum L.)

Terminal heat tolerance is an important breeding target in wheat. Methods of selection for heat tolerance in wheat are limited. The most common approach is the evaluation of yield in nurseries grown under heat stress. The objective of this study was to estimate inheritance of heat tolerance and the grain character in bread wheat by combining molecular marker analysis. The tolerance in bread wheat using a cross between genotypes that were identified previously were utilized to identify SSR markers that are linked to traits associated with terminal heat tolerance. Grain wt. was used as a measure of heat tolerance because this trait was highly correlated with tolerance levels of genotypes. Genotypes WH730 and RAJ4014 were used as tolerant and sensitive parents respectively for generating mapping populations against the study of terminal heat stress respectively. A Recombinant Inbred Line (RIL) mapping population derived from the heat sensitive genotype RAJ4014 and heat tolerant genotype WH730 was evaluated for the heat stress over two years in a replicated trial under timely sown (TS) and late sown (LS) field conditions. The parental lines were screened with approximately 300 SSR (μsatellite) markers out of which about 20% showed polymorphism. Parents and their Recombinant inbred lines (RILs) screened by microsatellite markers for finding allelic variation. Xgwm48, Xgwm55 and Xcfd29 are three markers suggested an application of marker-assisted selection for wheat improvement under terminal heat tolerance.

Managing Abiotic Stresses in Wheat

Wheat, a major staple crop of the world as well as of India, provides food and nutritional security to millions of the global populace. While the rate of genetic gain in productivity during the recent years has not been as impressive as in the past, the cultivars under development are being tailored to meet the demand for higher production together with the challenges imposed by several abiotic stresses such as high temperature, restricted access to irrigation water, drought, salinity/alkalinity, waterlogging, mineral deficiency, crop lodging and preharvest sprouting. Since the conventional approaches being practiced for wheat improvement will not be sufficient to achieve the productivity targets, it is essential to integrate the modern approaches leveraged by advances in phenomics, molecular biology, functional genomics, etc. Furthermore, stress mitigation options particularly through agronomic interventions are also essential to stabilize the productivity in wheat. Recent efforts being attempted in this direction have been highlighted in this article.

Complex G × E Interactions and QTL Clusters Govern End-Use Quality Traits in Hexaploid Wheat

Evaluation of wheat end-use quality in terms of loaf volume (LV) requires enormous time and labor inputs. Hence, many studies have attempted to use grain, flour and dough properties to predict LV. Many quantitative trait loci (QTL) underlying these traits have also been identified to facilitate breeding. However, correlations between such predictive tests and LV as well as their QTLs could be influenced by the environment. In this chapter, we review recent literature on the correlations and G × E interaction (GEI) of the bread making quality traits grain protein content (GPC), sodium dodecyl sulphate sedimentation volume (SV), dough rheological traits (DRT) and LV. We briefly discuss our results from the evaluation of a hexaploid wheat recombinant inbred line population for GPC, SV, LV and nine DRT by mixograph analysis in six year-location environments in India, which revealed that correlations between DRT and LV were not stable across environments. In addition, GEI measured in terms of principal components using Additive main effects and multiplicative interaction model showed up to 47 % contribution to the total variation of the traits, which was reflected in the location-specificity of QTLs expressed in single as well as multiple environments. Even though 16 QTL clusters for four to seven traits were identified, only one of them involved LV. The strong influence of the environment on complex interrelationships between DRT and the other end-use quality traits suggested that during breeding for wheat end-use quality, marker-based selection of these traits would be more efficient if specific agro-climatic zones are targeted separately.